Harsh Bais, PhD

RESEARCH


 

Carbon-based Electronics

image 1Realizing continued performance gains in Si CMOS technology by channel length scaling is becoming increasingly challenging due to the growing importance of short-channel effects such as fringe capacitance parasitics, degraded electrostatics, and gate leakage. To overcome these effects recent efforts in Silicon technology include the development of a double-gate or finFET architecture to improve device parasitics and boost device transconductance, integration of high-k gate dielectrics to reduce gate leakage, and uniaxial strained silicon channels to boost ballistic velocities. Alternatively there has been intense interest in pursuing carbon-based electronics, i.e. carbon nanotubes and graphene, in an effort to beat the performance limitations intrinsic to silicon.

image 3Graphene is a 2-D sheet of carbon atoms and has only very recently been explored as an electronic material. It is a zero-bandgap semiconductor with a linear E-k dispersion relationship, making it a very unique material. The advantages here, similar to carbon nanotubes, are very high mobilities and saturation velocities and the potential for nearly perfect two-dimensional electrostatics in field-effect devices. Despite the zero-bandgap nature of graphene, field-effect devices with Ion/Ioff ratios of approximately 10 can be constructed and many analog/RF applications of these devices can be pursued.

We maintain an interest in pursuing foundational research into the DC and high-frequency characteristics of graphene FETs. For example, we have demonstrated the first realization of saturating graphene-FET device characteristics with larger-than-unity current gains well up to the gigahertz regime; we developed a device model for these novel FETs under high bias; and performed the first study of channel-length scaling effects down to 100 nm channel lengths, demonstrating the viability of graphene-based electronics to compete with existing silicon technology.

illustrationOur recent focus has been on further improving graphene-based technologies by developing techniques to engineer ultra-high performance devices. We developed a novel graphene/dielectric heterostructure that resulted in device performance with almost an order of magnitude improvement over previous graphene-FETs. Our dielectric, hexagonal boron nitride (an insulating isomorph of graphene), proves to be an ideal choice for graphene electronics and a successful result in quest of finding a complimentary dielectric for carbon electronics.

We are also actively exploring new ways to utilize the many unique electronic and physical properties of graphene for new device applications. For example, we are pushing the limitations of dual-gated bilayer graphene where a field tunable bandgap allows unprecedented in-situ engineering of device performance for both digital and analogue applications; by engineering novel graphene/dielectric heterostructures we are studying strongly interacting multi-layer graphene heterostructures as a possible new route towards quantum switching; and we are exploring the integration of graphene-FETs with unconventional substrates that may allow the utilization of carbon-based electronics with systems where it has been traditionally difficult to apply Silicon technology.

Related Publications:

  1. I. Meric, C. Dean, S. J. Han, L. Wang, K. A. Jenking, J. Hone, and K. L. Shepard, "High-frequency performance of graphene field effect transistors with saturating IV-characteristics," International Electron Devices Meeting, 2011, pp. 2.1.1-2.1.4.
  2. I. Meric, C. R. Dean, A. F. Young, N. Baklitskaya, N. J. Tremblay, C. Nuckolls, P. Kim, and K. L. Shepard, "Channel Length Scaling in Graphene Field-Effect Transistors Studied with Pulsed Current−Voltage Measurements," Nano Letters, published online, January 27, 2011, doi: 10.1021/nl103993z
  3. C. R. Dean, A. F. Young, P. Cadden-Zimansky, L. Wang, H. Ren, K. Watanabe, T. Taniguchi, P. Kim, J. Hone, and K. L. Shepard, "Multicomponent fractional quantum Hall effect in graphene," Nature Physics 7, pp. 693-696, 2011.
  4. I. Meric, C. Dean, A. F. Young, J. Hone, P. Kim, and K. L. Shepard, "Graphene field-effect transistors based on boron nitride gate dielectrics," International Electron Devices Meeting, 2010.
  5. C. R. Dean, A. F. Young, I. Meric, C. Lee, L. Wang, S. Sorgenfrei, K. Watanabe, T. Taniguchi, P. Kim, K. L. Shepard, J. Hone "Boron nitride substrate for high-quality graphene electronics," Nature Nanotechnology 5, 722-726, 22 August 2010.
  6. I. Meric, N. Baklitskaya, P. Kim, and K. L. Shepard, "RF performance of top-gated, zero-bandgap graphene field-effect transistors," International Electron Devices Meeting, 2008.
  7. I. Meric, M. Y. Han, A. F. Young, B. Ozyilmaz, P. Kim, K. L. Shepard, "Current saturation in zero-bandgap, top-gated graphene field-effect transistors," Nature Nanotechnology, doi:10.1038/nnano.2008.268 September, 2008, pp. 1-6.